1. Field
Apparatuses and methods consistent with exemplary embodiments relate to a magnetic resonance imaging (MRI) apparatus used to diagnose various diseases using magnetic resonance (MR) images and a method of acquiring a functional image using the same.
2. Description of the Related Art
MRI apparatus generates images representing the density of atomic nuclei and physical and chemical properties by causing nuclear magnetic resonance of hydrogen atomic nuclei in the body using radio frequencies (RF) as specific ionization radiation and magnetic fields that are not harmful to humans.
MRI apparatuses are used to diagnose the patients by applying a predetermined frequency and energy to atomic nuclei under influence of a predetermined range of a magnetic field and converting energy emitted from the atomic nuclei into signals.
A proton is a constituent of an atomic nucleus and has a spin angular momentum and magnetic dipoles. Therefore, atomic nuclei are aligned in the direction of a magnetic field applied thereto and perform precession in the direction of the magnetic field. Thus, an image of a human body may be acquired via nuclear magnetic resonance.
Although MRI apparatuses are widely used to image the anatomical structure of a human and diagnose diseases, in recent years, attempts to form images representing functions of body organs, in particular functions of the brain, have been made. A representative example is functional MRI (fMRI).
The specific areas of the brain have specific functions, and consequently local cerebral blood flow and metabolism of the areas may increase when performing the specific functions. Functional MRI induces local nerve activation of the brain using such physiological variation, and thereafter represents a position of a corresponding function as an image. Functional MRI may exhibit more superior space and time resolution than positron emission tomography (PET), and may be repeatedly executed because injection of an isotope is not required.
Although there are various functional MRI methods, a blood oxygen level-dependent (BOLD) method is the most widely used. Local blood flow increase caused by activation of the brain means an increased amount of oxygen supplied to activated brain tissues. In this case, the increased supply of oxygen increases the amount of oxyhemoglobin in capillaries and veins, causing a reduction in the density of deoxyhemoglobin. Since deoxyhemoglobin is a paramagnetic material that reduces a T2 relaxation time of the surrounding area, a reduction in this material causes an increase of signals in a T2 weighted image.
However, if motion of a patient occurs during scanning for functional MRI, images representing functions, i.e., functional images acquired by a functional MRI, may have artifacts. Although the correction of such artifacts has been carried out via image processing, such as registration of the functional images, the functional images provide insufficient anatomical information for accurate correction of artifacts caused by patient motion.